As you say - especially with the NPPL - there is, in many way, no real advantage in having a microlight version of many of these three-axis aircraft. The NPPL allows you a microlight-type cheap medical and light aircraft style loadings.
one advantage as I see it, NPPL wise, is, you can fly to Europe with a microlight, but not in an SEP, / VLA
so same airplane, say Eurostar, under 450, no probs, fly to most of Europe
same machine, but not the microlight version, sure you can legally carry more weight, but with an NPPL your restricted to UK only, although I believe you can ask the CAA for permission to fly further,